Epstein-Barr virus (EBV) infection is an important cause of lymphomas in AIDS patients, especially in central nervous system lymphoma (CNS lymphoma). EBV transforms human primary B cells in vitro, the process of which is believed to resemble EBV transformation in vivo in AIDS-associated CNS lymphoma. How EBV regulates cellular genes to achieve the transformation remains unclear. Interferon regulatory factor-4 (IRF-4) is a member of the IRF family that has oncogenic potential. IRF-4 is highly expressed in EBV-transformed primary B cells in vitro, and high IRF-4 expression is associated with EBV in primary CNS lymphomas. Furthermore, down-regulation of IRF-4 results in apoptosis in EBV-transformed cells, and restore the IRF-4 expression prevented the growth inhibition of endogenous IRF4-kncokdown cells. Thus, IRF-4 is a critical factor involved in EBV-transformation, and a potential therapeutic target for EBV-associated tumors in vivo;however, the anti-apoptotic mechanism of IRF-4 in EBV transformation is unknown. Our long-term goal is to understand the role of cellular factors in viral transformation. The more immediate goal of this application is to determine the anti-apoptotic mechanisms of IRF-4 in EBV-transformed B lymphocytes. Apoptosis is roughly classified as intrinsic and extrinsic pathways. EBV induces some anti-apoptotic Bcl-2 family members that are capable of prevention of the intrinsic apoptosis pathway, and uses several viral proteins to block the functions of p53, a potential intrinsic pathway inducer. We thus hypothesize that an intrinsic apoptosis pathway may be activated but blocked by IRF-4 during EBV transformation. We will determine the mitochondria integrity and some hallmark caspase activities after IRF-4-knockdown to distinguish the two pathways. Whether specific inhibitors of caspases and other critical molecules involved in apoptosis rescue IRF-4-knockdown cells from apoptosis will be examined. These experiments may identify the apoptosis. These experiments may identify critical mechanisms that IRF-4 uses to prevent apoptosis in EBV-transformed cells.